The present invention relates to a lithographic printing plate precursor, more specifically, the present invention relates to a lithographic printing plate precursor suitable for the drawing of an image by a laser ray.
For the lithographic printing plate precursor, a PS plate comprising a hydrophilic support having provided thereon an ink-receptive photosensitive resin layer has heretofore been widely used. According to the plate-making process therefor, a plate is subjected to mask exposure (surface exposure) through a lith film and then the non-image area is dissolved and removed to obtain a desired printing plate.
In recent years, digitization technologies of electrically processing, storing and outputting image information using a computer have been widespread. To cope with this digitization technology, various new methods for outputting an image have been proposed and put into practical use. In pace with this tendency, demands are increasing for a computer-to-plate (CTP) technique capable of directly producing a printing plate by scanning a ray having high directivity, such as laser ray, according to the digitized image information without any intervention of a lithographic film. Thus, it is an important technical matter to obtain a printing plate precursor suitable therefor.
As one system for obtaining a lithographic printing plate precursor by scanning exposure, a constitution where a layer containing a photopolymerizable composition having excellent photosensitive speed is provided as a lipophilic (ink-receptive) photosensitive resin layer (hereinafter also called photosensitive layer) provided on a hydrophilic support and further an oxygen-cutting protective layer is provided, has been proposed and this is already available on the market. The lithographic printing plate precursor having such a constitution is facilitated in the development processing and can provide a printing plate having desired printing capabilities such as high resolution, good inking property and long press life.
However, the printing plate produced from this conventional high-sensitivity photopolymerization-type lithographic printing plate precursor has a problem in that due to insufficient adhesion between the image area and the support, the image area is slipped or thinned when a large number of sheets are printed, though this may vary depending on the use conditions.
Heretofore, for improving the adhesion between the support and a photopolymerizable photosensitive layer of a lithographic printing plate precursor, a method of providing an interlayer containing an organic phosphoric acid-base compound is widely known, but this is not sufficient in view of the press life.
JP-A-7-159983 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d) discloses a sol-gel interlayer containing a polymerizable group and JP-A-9-269593 discloses a sol-gel interlayer having further added thereto a phenolic compound or a phosphoric acid compound. These may surely give good adhesion but depending on the development conditions or the like, there is still a problem that the non-image area is scummed.
Accordingly, the object of the present invention is to provide a lithographic printing plate precursor which can overcome the above-described defects of conventional techniques and ensure both high adhesion and excellent scum resistance, particularly a lithographic printing plate precursor suitable for the drawing of an image by a laser ray.
As a result of extensive investigations to attain the above-described object, the present inventors have found that this object can be attained by providing an interlayer containing a polymer having a cationic group and a radical reactive group or an interlayer containing a compound capable of forming a complex with aluminum, between a support and a photopolymerizable photosensitive layer of a lithographic printing plate precursor. The present invention has been accomplished based on this finding.
More specifically, the present invention provides:
(1) A lithographic printing plate precursor comprising a hydrophilized aluminum support having provided thereon in sequence an interlayer and a photopolymerizable photosensitive layer, the interlayer containing a polymer having a cationic group and a radical reactive group and the photopolymerizable photosensitive layer containing a photopolymerization initiator, a compound having an addition polymerizable ethylenically unsaturated bond, and a polymer binder;
(2) A lithographic printing plate precursor comprising a hydrophilized aluminum support having provided thereon in sequence an interlayer containing a compound capable of forming a complex with aluminum and a photopolymerizable photosensitive layer containing a photopolymerization initiator, a compound having an addition polymerizable ethylenically unsaturated bond, and a polymer binder, the compound capable of forming a complex with aluminum giving a stability constant in the aluminum complex such that the common logarithmic value thereof is 3 or more;
(3) A lithographic printing plate precursor comprising a hydrophilized aluminum support having provided thereon in sequence an interlayer containing a compound capable of forming a complex with aluminum and a photopolymerizable photosensitive layer containing a photopolymerization initiator, a compound having an addition polymerizable ethylenically unsaturated bond, and a polymer binder, the compound capable of forming a complex with aluminum being a polymer; and
(4) The lithographic printing plate precursor as described in (3) above, wherein the compound capable of forming a complex with aluminum is a polymer having a structure represented by formula (I) or (II) on the side chain: 
xe2x80x83wherein R represents a hydrocarbon group having from 1 to 30 carbon atoms, which may have a substituent, Y represents a linking group to the polymer main chain skeleton, and Ar represents a heteroaryl group having one or more nitrogen atom, which may have a substituent.
One of the characteristic features of the lithographic printing plate precursor of the present invention is to provide an interlayer containing a polymer having a cationic group and a radical reactive group or an interlayer containing a compound capable of forming a complex with aluminum, so as to improve the adhesion between the photosensitive layer and the support. The lithographic printing plate precursor of the present invention can provide a printing plate favored with both long press life and excellent scumming resistance as compared with conventional printing plates using an interlayer containing an organic phosphoric acid-base compound or the like. The effect of the polymer having a cationic group and a radial reactive group is not yet clearly known, however, the following reasons may be considered. The polymer used in the interlayer has a cationic group, therefore, interacts with the anionic inorganic material on the substrate surface to exert firm adhesion to the substrate. The cationic group itself is hydrophilic and can be substantially removed by an aqueous developer, therefore, complete removal thereof can be attained on the unexposed area and no scumming is generated. On the other hand, on the exposed area, the radical reactive group forms a molecular bond with the photopolymerizable photosensitive layer and/or the radial reactive group itself due to the action of a radical generated upon exposure, therefore, the exposed area is gelled and cannot be removed by the developer and the high adhesion by the cationic group ensures a sufficiently long press life. From the standpoint of imparting sufficiently high adhesion and long press life, it is important in the present invention to use the compound having a cationic group and a radical reactive group as a polymer but not as a low molecular weight compound or oligomer.
The effect of the compound capable of forming a complex with aluminum is not yet elucidated, however, the following reasons may be presumed. The compound used in the interlayer coordinates to the aluminum on the substrate and forms a complex, whereby coordination to the aluminum metal on the substrate surface is attained and firm adhesion to the substrate is realized. The compound capable of forming a complex with aluminum adheres to the aluminum substrate by an interaction such as Coulomb force, therefore, can be substantially removed by an aqueous developer. In the unexposed area, the compound is completely removed, so that scumming does not occur. In the exposed area, the photosensitive composition of the upper layer is photocured and the developer does not permeate into the interlayer, so that the firm adhesion can be maintained.